The admin password can be added to the GameUserSettings.ini which can be edited from the config section of my.gameservers.com. Alternatively, this file can be found in the arkse/ShooterGame/Saved/Config/WindowsServer directory of your ftp.

1. Load the GameUserSettings.ini

2. Scroll down to [ServerSettings] (New servers may need to add this to the last line of the .ini file)